File:Human embryo day 18.jpg
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Human Embryo (day 18)
Approximate cross-section of a different, 18 day human conceptus (Carnegie stage 6).
Identify the
- 3 cavities - yolk sac, amniotic sac and chorionic sac.
- 3 layers of the trilaminar embryo - ectoderm (columnar cells), intraembryonic mesoderm (mesenchymal cells, endodermal cells (cuboidal single layer).
- extraembryonic mesoderm which surrounds the yolk and amniotic sacs, and continues to form the connecting stalk, where it then continues to line the chorionic sac. Extra- and intra-embryonic mesoderm merge along the perimeter of the embryonic disc.
- primitive groove with dense cluster of primitive streak cells below it.
At the top right of the micrograph is a secondary chorionic villus, lying in an empty maternal intervillus space. The villous has an outer layer of syncytiotrophoblast (smaller, darker nuclei), an intermediate layer of cytotrophoblast and a core of mesoblast (extra-embryonic mesoderm).
- Links: Carnegie stage 6
Reference
Nishimura etal., 1977
Cite this page: Hill, M.A. (2024, April 20) Embryology Human embryo day 18.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:Human_embryo_day_18.jpg
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
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